Could Starch Lines Be Culprit to Metal in Boxes?

Ray asks,

 Since April of this year we’ve been fighting with major metal detection rejections with one of our customer that has a stringent HACCP/SOP in place.

We feel we may have finally found the source of our metal contamination. We believe that it may be our metal starch lines and perhaps rust form the lines is mixing with the starch and being transferred to the products. We’re waiting for metal chemical analysis results to come back to confirm my suspicions.

While we are awaiting the results of the test we have come up with a few more questions and hope that you can help provide an answer.

Best Practices:

How often should starch lines be flushed?

Should straight bleach used?

What types of strainers are being used in the industry and what are considered the best systems?

Is anyone using inline magnets in their glue systems?

How often should the schedule 80 pipe lines be replaced, and is there anyone out in the industry using Predictive Maintenance to replace lines?

Is PVC piping a viable alternative for starch lines?

Thank you and your readers for any insight that can be provided.

Just a couple thoughts. Have you ruled out the chance of contamination from sources outside of the manufacturing process? Do the conveyors pass a maintenance shop grinders could be in use? Are there any RFID tags used in any of your processes?

For input on the starch lines I reached out to Wayne Porell at Harper Love Adhesives to see what experience he may have with such issues.­­­

First, I don’t have any plants having this issue. There may be more going on here than what we typically see.  Most well-run plants flush their starch lines at the end of every week by at least running water through the system after they shut down. Some plants also use Clean Tank HP™ from Walla Walla Chemical. Others just use bleach. However, bleach only disinfects the lines to help control bacteria. It doesn’t help remove any build up starch in the lines.

Some plants have strainers in place but remove the filter because they get clogged and cause the pan to over flow. These filters need to be cleaned, but can only be cleaned when there is no starch in the lines and the machine is down. You also want to make sure the filters are in place and are not damaged.

I don’t know of anyone using inline magnets to catch metal parts. If the plant is getting enough metal inside their boxes to set off alarms, then I would, as obviously they are, be looking where the metal is coming from. There shouldn’t be enough metal from mechanical pumps or bearings causing this issue. If there was, I would certainly think they would be seeing mechanical failures by now.

Over time schedule 80 iron pipes rust inside and create areas where starch can build up and harbor bacteria. This shouldn’t cause enough metal to come off to trigger an alarm. If anything, they rust through and cause leaks or the starch builds up inside the lines and creates flow issues at higher speeds.

The timeline for replacing these metal lines depends on the house keeping over the life of the lines. Like anything in the plant, the better that is taken, typically the longer it will last. The chemicals used to clean the lines can affect the longevity of the lines as well.

Schedule 80 PVC can be used and is used in some plants. The issue with these lines is you need to have hanger braces every four feet to keep them from sagging. If they sag, then you have areas where starch could build up in the lines. However, they are easier to clean if you keep them flushed on a weekly basis.

PVC lines also have to be braced well, especially if using pneumatic pumps for starch supply and return which tend to cause a pulsating action. PVC doesn’t allow bacteria to build up since it doesn’t have cavities like those caused by rust as in metal lines.

I have seen some plants switch to stainless steel lines. These are probably the best, but also cost the most.

 Again, if the plant is getting that many rejections due to metal they should review their whole process. Small specs of metal should set off alarms at their customers. Are they using any types of foil tape in their process?

— Ralph

3 Responses to “Could Starch Lines Be Culprit to Metal in Boxes?”

  1. Vann Parker Says:


    I tried to comment using the comment link, but when I completed my comment it wanted me to enter it using Twitter or Facebook or some other symbol. Well I don’t Twit or do Facebook so, I copied my comment and pasted it below.


    In our experience, the metal in corrugated boxes is most likely in the paperboard. We have two metal detectors that we have used many times when customers have had boxes or cartons kicked off filling lines due to metal being detected. We do a process of passing the cartons through our metal detectors, then we cut the samples into halves and we run each half separately through the metal detectors. We continue halving the samples and run them through the metal detectors until we get a postage stamp size remaining piece that tests positive. Then we take that piece to the microscope and dig out the metal.

    Any paper machine that does not have centrifugal cleaners will be susceptible to having heavy particles in the furnish. Most linerboard machines do not have centrifugal cleaners, so metal stays in the furnish. It could come from bullets in trees, from beakers dropped in the hydrapulper, or from other process sources. We have never seen metal in the corrugated board samples that appeared to have come in with the starch adhesive. That is not to say that it could not happen or that you could not have tramp metal attached to the board, but almost all the time the metal that we see is embedded in the paperboard, ie, down in the sheet and we dig it out.

    We will be glad to evaluate a box or boxes that have been kicked off a filling line for metal. By the way, sometimes we find that there is no metal in the box or carton that has been kicked off. That can happen also.


  2. Ron Mines Says:

    I agree with Vann. Also consider if you are using recycled paper that there is a potential for aluminium foil to be retained in the pulp and this could activate a metal detector

  3. Juan Javier Gonzalez Padilla Says:

    We had that problem when using some cheap recycled medium

    Changed the medium and problem solved


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